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Prashant K. Lalwani, Malu D. Devadasan / International Journal of Engineering Research and

Applications (IJERA) ISSN: 2248-9622 www.ijera.com

Vol. 3, Issue 3, May-Jun 2013, pp.108-112

108 | P a g e

Reduction Of Cod And Bod By Oxidation: A Cetp Case Study

Prashant K. Lalwani *, Malu D. Devadasan ***Asst Professor in Civil Engineering Department, Ganpat University, Gujarat-384012, India

** Asst Professor in Civil Engineering Department, Ganpat University, Gujarat-384012, India

ABSTRACTThe present study is focused on a

Common Effluent Treatment Plant (CETP)

located at Umaraya, District Baroda. Waste

water from about thirty five small and medium

scale industries majorly comprising of chemical

manufacturing and pharmaceutical industries are

treated in this CETP. The incoming wastewater

was collected and segregated into three groups asper their BOD/COD ratio. They were then

oxidized independently by two oxidants Fentons

reagent (Fe2+/H2O2) and Sodium Hypochlorite(NaOCl) and reduction in COD and BOD were

observed at different chlorine, H2O2, FeSO4doses,

different pH values and contact time for

determining the optimum values. COD and BOD

values at optimized conditions for the two

oxidants were compared and observed that

maximum reduction of 64.35% and 68.57%

respectively was achieved by Fentons reagent.The results clearly indicate that conventional

system should be replaced by advanced oxidation

process and Fentons reagent is a suitable choice.

Keywords - CETP, COD and BOD reduction,Fentons Reagent, Optimum Conditions, Oxidation

I. INTRODUCTIONDuring the last few years the concept of

CETP for the different small and medium scaleindustrial estates in the Gujarat state has developed

with a great speed. One of these CETP has beenestablished for the cluster of industries in westernside of Baroda district particularly between Padra

Taluka and Jambusar Taluka. M/s EnviroInfrastructure Co. Ltd. (EICL), village Umaraya,

Taluka Padra has set up a Common EffluentTreatment Plant (CETP). The plant is located onEffluent Channel Road. The CETP wascommissioned on 1st May 2000. CETP was set upto cater Small and Medium scale industries situated

in and around Padra & Jambusar Districts.These small scale industries go on

expanding and as per the market demand theychange their processes also. Therefore the composite

wastewater strength on which a CETP is designed isalso getting changed in every couple of years.Because of these changes in the parameters of the

composite wastewater it is observed that the present

CETP is not able to treat the composite effluent inan efficient manner. It may happen that the entire

biological treatment along with the primary

treatment also gets totally and /or partially

disturbed. The study here is aimed for somemodifications in the CETP, for maintaining two ofthe important parameter COD and BOD of the

treated waste water from CETP as they do not meetthe required GPCB (Gujarat Pollution ControlBoard) disposal standards to discharge into ECP(Effluent Channel Pipe) which is a closed effluent

channel that carries the effluent to Bay of Cambay.This is achieved by oxidizing the

wastewater independently by two oxidants viz.Fenton reagent (Fe

2+/H2O2) and Sodium

Hypochlorite (NaOCl) and comparing the results ofCOD and BOD reduction between them. Such

advanced physico-chemical processes, can takemuch higher fluctuating load and characteristics ofinlet effluent as compared to conventional biological

treatment methods.

1.1 Field StudyAt present, there are 52 member units, out

of which only 35 member industries are dischargingtheir waste water at CETP. As only 35 industries are

working the study is carried out only for compositewaste water of these industries, discharged intoequalization tank of CETP. The following Table 1shows the type of industries and their effluentcontributions.

Table 1 - Category of Industries and theircontribution to the CETP

Sr.

NoCategory

No of

Industries

Effluent

flow

(m3/d)

1Chemical manufacturingindustries

25 144

2 Pharmaceutical industries 8 446

3Glass manufacturingindustries

1 10

4 Others 1 0.4

Total flow 600.4

1.2 Present Condition of the CETPCETP at Umaraya is provided for treatment

of about 52 member industries. The present CETP isdesigned for 2250 m3/d of flow. The present CETP

needs modification because though the quantity offlow is very less (600.4 m3/d) than the designedcapacity, the parameters like COD, BOD, NH3-N,

SS and oil & grease after final treatment comes outto be 450,150, 87.8, 484 and 25mg/L respectivelywhich do not meet the GPCB disposal standard into

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ECP which are 250,100, 50, 100 and 20 mg/Lrespectively.The effluent is received from different industries

through a rubber lined tanker. Before the effluent isloaded in the equalization tank, the effluentparameters are measured and then only effluent is

loaded in the equalization tank. From here, theeffluent is lifted to Flash Mixer. At this tank,continuous dosing of hydrated lime and AluminumSulfate (Alum) slurry is added for flocculation and

coagulation. After mixing, the effluent is transferredto Primary Settling Tank. As per original treatmentscheme (2250 m3/day), two stage Aeration followed

by Secondary Clarifier treatment process wasprovided. As the present effluent quantity is veryless only one compartment of Aeration Tank is used.At tertiary treatment level, four Dual Media Filter

tanks and chlorination unit is provided.Generally, conventional biological

treatment such as activated sludge is only able todegrade below 1000 mg/L of COD. Thus, analternative treatment or pre-treatment of thewastewater is required. There are many treatment

options available for the removal of pollutantssuccessfully such as stripping, carbon adsorptionand membrane process. However, due to cost

effectiveness, stringent regulatory limits and processlimitations, advanced oxidation process (AOP) is aflexible technique towards enhancing the existingsystem. AOP is capable of improving thebiodegradability of complex or recalcitrantcompounds. This process is based on the chemical

oxidation technologies that use hydroxyl radical(OH) generated in situ. The radical oxidizes theorganic and/or inorganic contaminants to produceenvironmentally friendly fragments and eventuallyto CO2and H2O if sufficient reagents and time are

allowed. There are various ways of generatinghydroxyl radical and one such method is usingFentons reagent. Fentons reaction is based on the

catalyzed decomposition of hydrogen peroxide byFerrous ions (Fe

2+) to produce very reactive

hydroxyl radicals [1]:

Fe2+

+ H2O2 Fe3+

+ OH-+ OH

II.

MATERIALSANDMETHODS2.1 Materials

All chemicals employed in this study wereanalytical grade. All solutions were prepared indistilled-deionized water made on each experimental

day. Glassware used in this work was soaked withHNO3 (~10%) for 24 h, and rinsed with distilled-deionized water prior to drying. A chlorine stock

was made from 12% (100ml=12mg) sodiumhypochlorite (NaOCl). Hydrogen peroxide wasprepared by using the analytical grade (30% by wt.)

H2O2 as purchased. The ferrous sulphateheptahydrate (FeSO4.7H2O) was used as the sourceof Fe2+ in the Fenton process. Solutions of NaOHand HCl were used for pH adjustments.

2.2 Sample PreparationSampling and analysis of the raw waste

water coming from different industries was done by

taking grab sample. The waste water sample wascollected directly from tanker on approximatelyweekly basis for segregation purposes. The raw

waste water sample was first collected and analyzedfor different parameters to determine the quality ofthe incoming raw waste water and then wassegregated into three groups as per BOD/COD ratio

as shown in Table 2. Segregation of effluent meansseparation as per effluent characteristics. It is a newconcept for wastewater minimization and optimizes

the operation cost [2].

Table 2 - Various Industries Categorized in Groups

Group BOD/COD Flow rate

A < 0.30 480.00 m3/day

B 0.30-0.40 90.00 m3/day

C >0.40 70.00 m3/day

2.3 Experimental Procedure

2.3.1Oxidation by Sodium HypochloriteBatches of 100 ml volume of wastewater

sample of the three groups A, B and C were

prepared. Chlorine solutions of known strength wereprepared in de-ionized water in the range ofconcentration 2, 4, 6, 8, 10 ml. The residual chlorine

was found for the different chlorine concentrationsby iodometric method. Then by using the optimumchlorine dose obtained for the three groups residualchlorine for varying pH from 4-7 was found.

Residual chlorine graph for varying chlorine dosesand pH was plotted as shown in Fig.1. Using theoptimum chlorine dose and pH range found for thethree groups, COD and BOD of the wastewater after

chlorination was determined by standard methodsand graph was plotted as shown in Fig.6. All thesamples were kept in the dark during chlorination to

prevent photolysis.

2.3.2 Oxidation by Fentons ReagentFor various batches of 100 ml volumesamples of wastewater for three groups A, B, C,COD and BOD was determined by standard

methods for varying doses of H2O2 (1,3,5,10ml) toobtain optimum dose. 1mg fixed amount of solidferrous sulfate was added to the solution and mixeduntil complete dissolution. The contact time, pH and

temperature was kept constant to 40 minutes, 7.5and 30

oC respectively. Similarly the process was

repeated for obtaining optimum pH and contact timeby using optimized H2O2dose, pH, and contact timeas experiments proceed and keeping all other

quantities constant. The graphs of COD and BODwere plotted as shown in Fig. 2,3, 4 & 5.Then by

using all the optimized parameters obtained above

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COD and BOD was again determined and graphwas plotted (Fig.6).

Similarly, 100 ml volume sample was

prepared by mixing A, B and C group wastewaters.There initial COD and BOD was measured and thentreated with different H2O2dose (3, 4,5ml) to obtain

optimum dose using 1mg FeSO4, 4 pH, 60 mincontact time and 32

oC temperature. This process

was repeated using optimum H2O2dose for varyingFeSO4dose (0.5, 1, 1.5, 2mg) and graph was plotted

(Fig.7). The sludge formation was 3ml.

III. RESULTSANDDISCUSSIONAfter optimization of chlorination and

Fentons reaction, COD and BOD reduced for threesegregated groups of wastewater by both processescan be compared. Figures 3 and 10 shows the initialCOD and BOD level and reduced levels aftertreatment. The COD reduction during chlorination

was 23.2%, 19.16%, 45.14% while BOD reductionwas 38.91%, 24.27%, 44.67% [3]. Whereas theCOD and BOD reduction during Fenton treatmentwas 50.86%, 49.47%, 60% and 34.55%, 49.33%,

56.67% respectively. Furthermore COD and BODreduction during Fenton treatment of mixedwastewater at optimized pH, H2O2 and FeSO4

dosing was found to be 64.35% and 68.57%respectively [4, 5]. The results obtained clearlyindicates that there is no significant difference

between the COD and BOD reductions forsegregated and mixed wastewater but rather theFentons reagent was more effective for combined

wastewater. Thus in this case segregation conceptcannot be applied. The reduction in other parameterslike NH3-N, SS and oil & grease after treatmentwith Fentons reagent of mixed wastewater cameout to be 45.76%, 75.43% and 17.32% respectively.

It is obvious from the above data that CODand BOD reduction was achieved maximum duringFentons treatment. The optimum pH, contact time,

H2O2and FeSO4dosing was found to be 4, 60 min,4ml and 1mg respectively at temperature 32oC forthe mixed wastewater [6]. The reduction achieved

by oxidation process was more than that achievedby conventional biological treatment at CETP. It

shows that the organic loading coming from thechemical and pharmaceutical industries is majorly

of non-biodegradable type. In any case 100 per centoxidation could not be achieved because all theadded oxidant molecules may not be available for

the oxidation of organic matter contributing toCOD. A portion of oxidant might have also beenused in the oxidation of some other metals (in low

concentrations) in the sample [7].

IV. CONCLUSIONFrom the above experiments we can

conclude that conventional biological treatment ofthe CETP should be replaced with physico-chemicalprocess like advanced oxidation process as

incoming COD value is more than 1000mg/Lmajorly consisting of non-biodegradable load. Thestudy showed that among the two oxidants Sodium

Hypochlorite and Fentons reagent, the latter is themost efficient as the maximum COD and BODreduction was observed for this oxidant.

Figure 1: Residual Chlorine for varying Chlorinedoses and pH values

Figure 2: Optimization of H2O2 dosing

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Figure 3: Optimization of pH

Figure 4: Optimization of Contact Time

Figure 5: Optimization of pH

Figure 6: Comparison of Chlorination and Fentonstreatment process at optimized conditions

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Figure 7: Optimum H2O2 and Iron dosing for mixedwastewater

V. ACKNOWLEDGEMENTSThe authors would like to acknowledge CETP

Umaraya for the assistance rendered.

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and A. Aziz Omar, Using FentonsReagents for the Degradation ofDiisopropanolamine: Effect of

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12-17.[2]

Metcalf and Eddy, WastewaterEngineering: Treatment and Reuse (Tata

McGraw-Hill, Fourth edition, 2003).

[3]

F. Vaezi, K. Naddafi, F. Karimi and M.Alimohammadi, Application of chlorinedioxide for secondary effluent polishing,

International Journal of EnvironmentalScience & Technology, 1(2),2004, 97-101.

[4]

Qingxuan Zhang and Guohua Yang, The

removal of COD from refinery wastewaterby Fenton reagent, IEEE Conference(RSETE),China, 2011, 79747977.

[5] Lech Kos, Karina Michalska and JanPerkowski, Textile Wastewater Treatmentby the Fenton Method,Fibres & Textiles in

Eastern Europe, 18 (4),2010, 105-109.

[6]

Cludia Telles Benatti and Clia ReginaGranhen Tavares, Fentons Process for theTreatment of Mixed Waste Chemicals, in

Dr. Tomasz Puzyn (Ed.), OrganicPollutants Ten Years After the StockholmConvention - Environmental and Analytical

Update,(InTech, 2012) 247-270.[7]

M. Ali Awan, Reduction of chemicaloxygen demand from Tannery wastewater

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